The invention generally relates to gas concentrators, and more particularly relates to medical oxygen concentrators used by patients in the home care setting where cost and frequency of maintenance performed by a technician should be minimized.
The application of oxygen concentrators for therapeutic use is known, and many variants of such devices exist. A particularly useful class of oxygen concentrators is designed to be used in a patient's home or workplace without the assistance of a medical practitioner or caregiver. These home concentrators are typically referred to as stationary concentrators, as they are not designed to be carried by a patient, distinguishable from portable concentrators which are designed to be carried by a patient for most ambulatory activities. Most of these oxygen concentrators are based on Pressure Swing Adsorption (PSA), Vacuum Pressure Swing Adsorption (VPSA), or Vacuum Swing Adsorption (VSA) designs which feed compressed air to selective adsorption beds, sometimes also referred to as sieve beds. In a typical oxygen concentrator, the beds utilize a zeolite adsorbent to selectively adsorb nitrogen, resulting in pressurized, oxygen-rich product gas. This class of oxygen concentrator may also contain one or more systems to extend the service life of the equipment. These systems may include software algorithms to alter the PSA timing, input flow, or operating pressure to extend the performance of the adsorption beds as their capacity is reduced over its operating life as described in common inventors' prior disclosures U.S. Pat. No. 7,857,894 and its related applications incorporated in their entirety by reference. In these systems the adsorption beds may also include desiccant layers before the main adsorbent layer to remove water and other contaminants or dedicated water removal components such as membrane air dryers as described in common inventors' prior disclosures U.S. Pat. No. 7,780,768 and its related applications, incorporated in their entirety by reference.
The main elements in a typical home-use therapeutic oxygen concentrator are shown in FIG. 1. Air is draw in, and typically filtered, at air inlet 1 before being pressurized by compressor 2 to a pressure of 1.2 to 2.5 atmospheres. The pressurized air is directed by feed valve arrangement 9 through adsorbent beds 3. An exemplary adsorbent bed implementation, used in a concentrator design developed by the inventors, is two columns filled with a lithium exchanged zeolite adsorbent in the ratio of about 1 gram of adsorbent per 1-10 ml of oxygen produced. The pressurized air is directed through these adsorber bed columns in a series of steps which constitute a gas separation cycle, often a PSA cycle or some variation including vacuum instead of, or in conjunction with, compression yielding overall compression ratios of about 1.5:1 to 4.0:1. Although many different arrangements of adsorber vessels and gas separation cycles are possible, the result is that nitrogen is removed by the adsorbent material, and the resulting oxygen rich gas is routed 10 to a product gas storage device at 4. Some of the oxygen product gas can be routed back through the bed to flush out (purge) the adsorbed nitrogen to an exhaust 6. Generally multiple adsorbent beds, or columns in the exemplary device, are used so at least one bed may be used to make product while at least one other bed is being purged, ensuring a continuous flow of product gas. The purged gas is exhausted from the concentrator at the exhaust 6.
Such gas separation systems are known in the art, and it is appreciated that the gas flow control through the compressor and the adsorbent beds is complex and requires precise timing and control of parameters such as pressure, flow rate, and temperature to attain the desired oxygen concentration of 80% to 95% purity in the product gas stream. Accordingly, most modern concentrators also have a programmable controller 5, typically a microprocessor, to monitor and control the various operating parameters of the gas separation cycle. In particular, the controller controls the timing and operation of the various valves used to cycle the beds through feed, purge, and pressure equalization steps, which make up the gas separation cycle. Also present in oxygen concentrators is an output control system 7 which acts to ensure that the therapeutic output flow of oxygen is continuous and steady even during the pressure swings associated with the production of the oxygen. A typical oxygen concentrator will also contain a user/data interface 8 including elements such as an LCD display, alarm LEDs, audible buzzers, and control buttons. Portable oxygen concentrators would necessarily also include one or more battery packs for portable use.
To be conveniently used by an individual in a home or workplace environment needing therapeutic oxygen, the stationary home oxygen concentrators should be less than about 2100 cubic inches and preferably less than 1600 cubic inches in total volume, less than about 25 pounds and preferably less than 20 pounds in weight, and produce less than about 45 decibels of audible noise, while retaining the capacity to produce a flow of product gas adequate to provide for a patient's oxygen needs, usually a flow rate prescribed by a medical practitioner in about the range of 1 LPM to 5 LPM. Although stationary PSA based concentrators have been available for many years, such fixed site units may weigh 30-50 pounds or more, be several cubic feet in volume, and may produce sound levels greater than 45 dBA. Thus they are loud and difficult to move around. To achieve these beneficial improvements in noise and size/weight, improved home oxygen concentrators involve a significant amount of miniaturization and efficiency improvements, leading to smaller, more complex designs compared to older designs. System size, weight, and complexity may lead to fewer mitigative options or design choices against contamination and other wear and tear effects that can lead to an unacceptably short maintenance interval, and therefore require novel design features to achieve both the improvements in size and noise while maintaining adequate lifetime.
It is therefore necessary to design home oxygen concentrators such that zeolite contamination is handled in a manner that avoids costly or frequent maintenance by a field technician or equipment provider. The inventors have previously disclosed a system that achieves long sieve bed life by removing water prior to the feed gas as described in the above cited references. This approach may desirable for some portable oxygen concentrators where the beds are even smaller than a home based stationary system, but because of the cost involved, may not be appropriate to stationary home based system where the price point needs to be very low. It is therefore desirable to design a home oxygen concentrator that minimizes size and weight and cost as a function of oxygen output with commonly available commercial adsorbents such as Z12-07 manufactured by Zeochem or Oxysiv MDX manufactured by UOP. While eliminating water removal components such as membrane air dryers or pretreatment layers such as activated alumina or a NaX type zeolite will reduce the cost of the adsorbent beds it will also reduce the service life of the beds to an unacceptable level. Oxygen equipment used for Long Term Oxygen Therapy (LTOT) is optimally deployed for 3-5 years without any service requirements. Any service requirement within that time interval simply adds to the overall cost of the equipment, which substantially reverses any cost benefit gained by removing a membrane air dryer or pretreatment layer. Further, allowing sieve bed contamination without prevention or service may lead to providing 82-87% purity oxygen instead of 87-95% pure oxygen to the patient. To reduce the overall cost of delivering oxygen therapy, devices must be designed that do not require field service by a technician or equipment provider, and also minimize the cost, size, power consumption, and noise of the equipment that is used inside of the patient's home.
A typical adsorbent bed or adsorber is constructed of a column with an inlet port and an outlet port arranged at opposite ends. The adsorbers would typically be connected to the valve manifold of the concentrator through tubing or a direct manifold connection. Either prior art construction method resulted in a robust pneumatic connection that was only meant to be disconnected by a trained service technician who could access the internal components of the concentrator and disconnect or disassemble the inlet and outlet connections. Some columns, such as those that are adhesive bonded to an integrated manifold, may not be removable at all in a field service environment and must be replaced in combination with other system components to achieve zeolite replacement. Therefore user-replaceable adsorber beds are desirable and provide an approach that may increase the service life of a concentrator without the costly water removal components and without the need for factory or factory trained service. Techniques for producing a medical concentrator of the portable type with user replaceable adsorber beds are described in U.S. application Ser. Nos. 13/016,706 and 13/449,138 by common inventors and incorporated in their entirety by reference